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Commonlines, or Aristotelian topoi, are general lines of reasoning that reflect patterns of thought—in other words, commonlines include methods of logic that most people would find convincing. Examples include appealing to authority, offering examples, and/or examining evidence. Commonlines, when used properly, form the basis of a coherent argument. Below is a complete list of commonlines, from Aristotle’s Rhetoric, II.23. Examples of commonlines are also provided.

1. Argument from Opposite: Sometimes, it’s difficult to explicitly prove the point we want to make. One way around this is to consider the opposition: if the complete opposite of our claim is bad, then our claim must be good.

“If war is the cause of our present troubles, peace is what we need to put things right again” (Aristotle Rhetoric II.23).

This example, of course, implies that the audience already agrees that war is the cause of trouble, or that a good portion of our argument will be convincing them of this fact.

2. Argument by Definition: All words have connotations—words like “socialism,” “democracy,” or “totalitarian” are frequently associated with moralistic values that are included in their definition. Sometimes, the key part of an argument is convincing the opposition that a certain word does not mean what they think it means. The first step in accomplishing this is to clearly define the word in contention.

“‘Just’ does not always mean ‘beneficial,’ since no one would consider it ‘beneficial’ to be ‘justly’ put to death” (Aristotle Rhetoric II.23).

Here, the writer is not trying to argue the claim “what is just is best for society;” instead, he/she makes the claim that what is just is not necessarily beneficial for an individual.

3. Argument by Complement: Many events or phenomena naturally come in pairs—if there is a receiver, there must be a giver; if there is a master, there must also be a servant; if created, there must be a creator. If we can provide irrefutable evidence of one, we prove the existence of the complement “pair.”

“If it is right for our leader to command our obedience, it is also right that we obey the command” (Aristotle Rhetoric II.23).

CAREFUL, though! We should still consider each statement separately, to determine that they’re actually complements. If we want to make the aforementioned claim, we must prove the relation between the first and second claims.

4. Argument by Comparison: This argument goes something like this—if a claim that is unlikely turns out to be true, then a related claim that is more “truthful” is most certainly true.

If you can pass an exam after no sleep and no studying, then you can certainly pass that same exam after sleep and studying.

5. Argument by Consistency: Claims that if one is willing to offer something in order to accomplish a goal, he/she should be willing to follow up with the offer after the goal has been accomplished.

If someone values his/her pet dog at $1000 and the pet gets lost, he/she should be willing to pay $1000 if someone successfully finds and returns the lost pet.

6. Argument by Division: Dividing up your argument or a concept to make your argument clearer or more forceful. In dividing, it is important to understand the audience well and address the specific points of contention.

Credibility is determined by types of sources, quality of research, and number of citations. Researcher A is superior to Researcher B in all these aspects, making A more credible than B.

7. Argument by Example: Finding concrete, real-life cases to back up a claim is almost essential for any argument.

Cutting soda out of people’s diets makes them healthier, because Carla S. and the other fifty-six high school students lost weight and had more energy after they stopped drinking soda during the experiment.

8. Argument by Authority: Support from a widely-trusted and well-established authority figure can help bolster one’s claim. When using this argument, be aware of any individual biases these authority figures may have.

According to Robert Reich, Candidate A has the best economic policy for this country. Since Robert Reich is a renowned economist, it is likely that Candidate A does indeed have the best economic policy.

9. Argument by Distributio: Examining each part of a subject individually; by doing so, one gains a better understanding of the subject as a whole.

“An individual is prosecuted for slander against the gods. The defense responds with the questions ‘What temple has he profaned? What gods recognized by the state has he not honored?’” (Aristotle Rhetoric II.23).

In this example, by examining these two claims, the defense is examining two parts of the opposition’s argument (defendant has committed slander) separately in order to form a counterargument.

10. Argument by Consequence: Since A leads to bad consequences X, Y, Z, we should not do A. However, because all actions can have good and bad consequences, a successful argument may also have to examine why one type of consequence (good or bad) outweighs the other kind.

You shouldn’t smoke, because smoking causes respiratory problems, increases your chances of lung cancer, and exposes those around you to secondhand smoke.

11. Argument by “half-empty, half-full”: Arguing that A is good by examining the results of A in a positive light. Like the argument by consequence, one may also have to prove why thinking about something in a positive light is better than considering it in a negative light, or vice-versa.

“[You claim that learning public speaking is bad, because] if you say what is right, men will hate you; if you say what is wrong, the gods will hate you. On the contrary, you ought to take to public speaking: for if you say what is right the gods will love you; if you say what is wrong, men will love you” (Aristotle Rhetoric II.23).

12. Argument by Public vs Private: Argues that although someone (usually an authority figure) may publicly take a stand on a certain issue, he/she does not truly believe in his/her stance because his/her private life contradicts these espoused beliefs. When used effectively, this can be a good counter for the Argument by Authority; however, one has to show what this dissonance between public and private acts means about the authority figure’s personal views.

Although Al Gore claims to believe in global warming and claims that something should be done to reduce carbon emissions, the fact that he travels in a private jet indicates that he is not particularly serious about these beliefs.

13. Argument by Contrapositive: This is a commonly used logical structure. Generally, we want to prove that “if A, then B.” However, if this proof is too difficult, showing that “if not B, then not A” is logically equivalent.

“If foreigners can be made citizens as a result of their merit, then citizens ought to also be exiled if they perform irreparable harm to our society” (Aristotle Rhetoric II.23).

14. Argument by Motive: Similar to Argument by Public vs. Private, this argumentative technique claims that an individual’s motive for performing an action is not what it appears. This can be a powerful tool for discrediting an authority figure, or demonstrating that something “good” or “bad” is not what it may seem.

“God gives to many great prosperity, not because God is good towards them, but because it makes their eventual ruin more conspicuous” (Aristotle Rhetoric II.23).

15. Argument by Practicality/Parsimony: Very similar to argument by motive, but with the basic assumption that people are motivated to act on things that are “possible, easy and useful to ourselves or our friends or hurtful to our enemies.”

The accused claims he/she is innocent of murder because the deceased was a good friend; moreover, the victim lived 100 miles away from the accused, making it very inconvenient to commit the crime.

16. Argument by Likelihood: Basically states that if many people believe an unlikely phenomenon, then it is very likely that this phenomenon is true. Take extreme care when using this argument; double-check for cognitive bias (the bandwagon effect).

Although it seems unlikely that Oski and Stanford’s Tree would fraternize,  a crowd of outraged students claim to have seen them frolicking together in Eucalyptus Grove at midnight.

Note that in this example, the opposition can still question the reliability of witnesses; however, the presence of these witnesses undoubtedly strengthens the case.

17. Argument by Explanation: Explaining why a false perception exists. Note that this also involves disproving the logic behind the false perception and explaining why an alternative view is better.

It is commonly believed that cold weather makes people sick. However, the cold itself does not directly cause the illness; rather, it is the fact that, when the weather gets cold, people tend to “huddle up” and stay indoors more, making it easier for bacteria and viruses to spread.

18. Argument by Logical Progression: Often, when presented with a large list of possible causes and effects or precedents and antecedents, it is easy to mix which cause precedes which effect. The argument organizes each precedent with its corresponding antecedent and is useful if one’s argument is logically sound.

“When the people asked Xenophanes [a philosopher]…if they should or should not sacrifice to Leucothea [a sea goddess] and mourn for her, he advised them not to mourn for her if they thought her a goddess, and not to sacrifice her if they thought her a mortal woman” (Aristotle Rhetoric II.23).

Here, Xenophanes notes that the people’s preceding action does not logical match their conclusion, and he points it out as such.